MMMasato Minamitsuji

Masato Minamitsuji

Osaka Butsuryo University
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Masato Minamitsuji has a total of 260 co-authors. Here are the top co-authors by number of shared publications:

Latest Publications

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    Erratum: Effective description of generalized disformal theories

    by Kazufumi Takahashi, Masato Minamitsuji, Hayato Motohashi

    Cited by 1
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    Exact p p -wave solutions in shift-symmetric higher-order scalar-tensor theories

    by Masato Minamitsuji

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    Review of: "Primary Hairs May Create Echoes"

    by Masato Minamitsuji

    The manuscript presents an important study on black holes with primary Proca-Gauss-Bonnet hair and their potential to generate echoes in the ringdown phase. The authors investigate the quasinormal spectrum of scalar and Dirac test fields in these bac...

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    Stealth black hole solutions in higher-order Maxwell–Einstein theories

    by Masato Minamitsuji

    In this paper, we study static and spherically symmetric black hole solutions in higher-order Maxwell–Einstein theories. We do not particularly focus on the degenerate classes of theories. For several specific choices of the coupling functions, we show that in the presence of the ordinary Maxwell kinetic term, the Reissner–Nordström–(anti-)de Sitter solution in the pure Maxwell–Einstein theory can also be a solution in generic classes of higher-order Maxwell–Einstein theories, and in the absence of the ordinary Maxwell kinetic term, the Schwarzschild–(anti-)de Sitter solution with the nonzero electric field can be obtained. This corresponds to a stealth black hole solution as the electric field does not affect the spacetime geometry. We then focus on several degenerate classes of higher-order Maxwell–Einstein theories, and find that the dyonic Reissner–Nordström–(anti-)de Sitter solution in the pure Maxwell–Einstein theory can be a solution.

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    Review of: "Inverting No-Hair Theorems: How Requiring General Relativity Solutions Restricts Scalar-Tensor Theories"

    by Masato Minamitsuji

    This manuscript presents a comprehensive and well-executed classification of higher-derivative scalar-tensor theories that admit General Relativity (GR) solutions as exact solutions. The authors focus on identifying subclasses of these theories—speci...

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    Even-parity black hole perturbations in minimal theory of bigravity

    by Masato Minamitsuji, Shinji Mukohyama, Michele Oliosi

    We study even-parity black hole perturbations in minimal theory of bigravity. We consider the Schwarzschild solution written in the spatially flat coordinates in the self-accelerating branch as the background solution. We clarify the gauge transformations for the ℓ=0, 1, and ≥2 modes with ℓ being the angular multipole moments under the joint foliation-preserving diffeomorphism transformation. Requiring that the asymptotic regions in the physical and fiducial sectors share the same Minkowski vacua, the solution to the ℓ=0 perturbations can be absorbed by a redefinition of the Schwarzschild background. In order to analyze the ℓ=1 and ≥2 modes, for simplicity we focus on the effectively massless case, where the constant parameter measuring the ratio of the proper times between the two sectors is set to unity and the effective mass terms in the equations of motion vanish. We also find that as a particular solution all the ℓ=1 perturbations vanish by imposing their regularity at spatial infinity. For each of the ℓ≥2 modes, in the effectively massless case, we highlight the existence of the expected two propagating modes and four instantaneous modes.

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    Black hole thermodynamics in generalized Proca theories

    by Masato Minamitsuji, Kei-Ichi Maeda

    We investigate thermodynamics of static and spherically symmetric black holes (BHs) in generalized Proca (GP) theories by applying the Iyer-Wald prescription. BH solutions in GP theories are divided into the two classes. The first class corresponds to the solutions obtained by the direct promotion of the BH solutions in shift-symmetric Horndeski theories, while the second class consists of the solutions which are obtained only in GP theories and contain a nonzero electromagnetic field. For BH solutions in the first class, we confirm that the BH entropy and its thermodynamic mass remain the same as those in the counterpart solution in shift-symmetric Horndeski theories. We also calculate the thermodynamical variables of the several static and spherically symmetric BH solutions in the second class and investigate the thermodynamical stability when there exist two BH solutions.

    Cited by 6
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    Angular and radial stabilities of spontaneously scalarized black holes in the presence of scalar-Gauss-Bonnet couplings

    by Masato Minamitsuji, Shinji Mukohyama, Shinji Tsujikawa

    We study the linear stability of spontaneously scalarized black holes (BHs) induced by a scalar field ϕ coupled to a Gauss-Bonnet (GB) invariant RGB2. For the scalar-GB coupling ξ(ϕ)=(η/8)(ϕ2+αϕ4), where η and α are constants, we first show that there are no angular Laplacian instabilities of even-parity perturbations far away from the horizon for large multipoles l≫1. The deviation of angular propagation speeds from the speed of light is largest on the horizon, whose property can be used to put constraints on the model parameters. For α≳−1, the region in which the scalarized BH is subject to angular Laplacian instabilities can emerge. Provided that α≲−1 and −1/2<αϕ02<−0.1155, where ϕ0 is the field value on the horizon with a unit of the reduced Planck mass MPl=1, there are scalarized BH solutions satisfying all the linear stability conditions throughout the horizon exterior. We also study the stability of spontaneously scalarized BHs in scalar-GB theories with a nonminimal coupling −βϕ2R/16, where β is a positive constant and R is a Ricci scalar. As the amplitude of the field on the horizon approaches an upper limit |ϕ0|=4/β, one of the squared angular propagation speeds cΩ−2 enters the instability region cΩ−2<0. So long as |ϕ0| is smaller than a maximum value determined for each β in the range β>5, however, the scalarized BHs are linearly stable in both angular and radial directions.

    Cited by 10
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    Black hole thermodynamics in Horndeski theories

    by Masato Minamitsuji, Kei-Ichi Maeda

    We investigate thermodynamics of static and spherically symmetric black holes (BHs) in the Horndeski theories. Because of the presence of the higher-derivative interactions and the nonminimal derivative couplings of the scalar field, the standard Wald entropy formula may not be directly applicable. Hence, following the original formulation by Iyer and Wald, we obtain the differentials of the BH entropy and the total mass of the system in the Horndeski theories, which lead to the first law of thermodynamics via the conservation of the Hamiltonian. Our formulation covers the case of the static and spherically symmetric BH solutions with the static scalar field and those with the linearly time-dependent scalar field in the shift-symmetric Horndeski theories. We then apply our results to explicit BH solutions in the Horndeski theories. In the case of the conventional scalar-tensor theories and the Einstein-scalar-Gauss-Bonnet theories, we recover the BH entropy obtained by the Wald entropy formula. In the shift-symmetric theories, in the case of the BH solutions with the static scalar field, we show that the BH entropy follows the ordinary area law even in the presence of the nontrivial profile of the scalar field. On the other hand, in the case of the BH solutions where the scalar field linearly depends on time, i.e., the stealth Schwarzschild and Schwarzschild-(anti–)de Sitter (AdS) solutions, the BH entropy also depends on the profile of the scalar field. By use of the entropy, we find that there exists some range of the parameters in which a Schwarzschild-AdS BH with nontrivial scalar field is more thermodynamically stable than a Schwarzschild-(AdS) BH without scalar field in general relativity. Finally, we consider the Horndeski theories minimally coupled to the U(1)-invariant vector field, where BH solutions contain the mass and the electric charge, and clarify the conditions under which the differential of the BH entropy is integrable in spite of the presence of the two independent charges.

    Cited by 21
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    Instability of scalarized compact objects in Einstein-scalar-Gauss-Bonnet theories

    by Masato Minamitsuji, Shinji Mukohyama

    We investigate the linear stability of scalarized black holes (BHs) and neutron stars (NSs) in the Einstein-scalar-Gauss-Bonnet (GB) theories against the odd- and even-parity perturbations including the higher multipole modes. We show that the angular propagation speeds in the even-parity perturbations in the ℓ→∞ limit, with ℓ being the angular multipole moments, become imaginary and hence scalarized BH solutions suffer from the gradient instability. We show that such an instability appears irrespective of the structure of the higher-order terms in the GB coupling function and is caused purely due to the existence of the leading quadratic term and the boundary condition that the value of the scalar field vanishes at the spatial infinity. This indicates that the gradient instability appears at the point in the mass-charge diagram where the scalarized branches bifurcate from the Schwarzschild branch. We also show that scalarized BH solutions realized in a nonlinear scalarization model also suffer from the gradient instability in the even-parity perturbations. Our result also suggests the gradient instability of the exterior solutions of the static and spherically-symmetric scalarized NS solutions induced by the same GB coupling functions.

    Cited by 27
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